1. Field of the Invention
The present invention relates to an anode containing silicon (Si) as an element and a battery using the anode.
2. Description of the Related Art
In recent years, as mobile devices have been sophisticated and multi-functionalized, the higher capacity of secondary batteries as a power source for these mobile devices has been demanded. As a secondary battery to meet such a demand, there is a lithium ion secondary battery. However, since graphite is used for the anode in the lithium ion secondary battery in practical use currently, the battery capacity thereof is in a saturated state and thus it is difficult to attain a vastly high capacity thereof. Therefore, it is considered to use silicon or the like for the anode. In recent years, forming an anode active material layer on an anode current collector by vapor-phase deposition method or the like has been reported (for example, refer to Japanese Unexamined Patent Application Publication Nos. 8-50922 and 11-135115, and Japanese Patent Publication No. 2948205). Silicon or the like is largely expanded and shrunk due to charge and discharge. Thus, it has been problematic that the cycle characteristics are lowered due to pulverization. However, by using vapor-phase deposition method or the like, pulverization can be prevented, and the anode current collector and the anode active material layer can be integrated. In the result, electron conductivity in the anode becomes extremely favorable, and high performance both in the capacity and in the cycle life is expected.
However, even in the anode in which the anode current collector and the anode active material layer are integrated, when charge and discharge are repeated, the anode active material layer is intensely expanded and shrunk. In the result, for example, the anode active material layer is dropped, and the cycle characteristics are lowered. Further, the anode current collector is deformed due to the stress of the expansion and shrinkage, and thus the battery is swollen. Therefore, it is considered that by adding a metal element such as iron that is not alloyed with lithium (Li) to the anode active material layer, the expansion and shrinkage of the anode active material layer are relaxed and the characteristics are improved (for example refer to Japanese Unexamined Patent Application Publication Nos. 2003-217574 and 2005-197080).